The incident occurred around 4:00 am (0200 GMT) in a small residential building.
The cause of the blast is still unknown and the explosion sparked a fire, said Gema Igual, mayor of Santander, capital of the Cantabria region.
"The building had a ground floor and two floors, where there could have been around 20 residents," Igual said.
Residents from neighbouring buildings were evacuated as a precautionary measure.Local emergency services said that 10 people were taken to hospital with two already released.
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